1. Field of the Invention
The present invention relates to power supplies which convert an input AC line voltage to a DC output voltage. In particular, the present invention is an improved linear power supply which has significantly lower capacitance and higher efficiency than prior art linear power supplies.
2. Description of Prior Art
The conventional form of linear DC power supply includes a step down transformer which has its primary winding connected to the input terminals of the power supply. The secondary of the transformer is connected to a rectifier circuit which rectifies the AC voltage induced in the secondary. The output of the rectifier circuit is a unidirectional charging current which is supplied to a filter capacitor. The size of the filter capacitor is selected so that the voltage across the filter capacitor is essentially a DC voltage with a small (for example one or two volts) ripple voltage riding on top of the DC voltage. For DC power supplies requiring high amperage output, the total filter capacitance becomes extremely large, which increases the cost and size of the power supply.
Non-linear or switching type power supplies have also been developed which exhibit high efficiencies. These switching power supplies, however, suffer from radio frequency (RF) and electromagnetic interference (EMI) problems due to the switching of semiconductor devices within the power supply circuitry during the operation of the power supply. As a result, switching type power supplies are undesirable in many applications.